Control system



Nov. 28, 1933. H. BANY ET AL 1,937,498

CONTROL SYSTEM Filed Feb. 26, 1932 Inventors: H erm an Bany, H arold TSeeley,

I TheirAttorney.

Patented Nov. 28, 1933 PATENT f OFFICE x CONTROL SYSTEM Herman Bany and Harold '1. Seeley, YeadomPa assignors to General Electric Company, a cor- H poration of New York Application February 26, 1932. Serial No. 595,320

11 Claims. (Grin-11a) Our invention relates to control systems and particularly to control systems for frequency converters and its object is to provide animproved arrangement for automatically controlling the connection of a frequency converter between two alternating current systems so that a large synchronizing-current does not flow when .the converter is interconnected between the two systems. Our invention will be better understood from Y the following description when taken in connection with the accompanying drawing the single figure of which diagrammatically illustrates a frequency converter control system embodying our invention and its scope will be pointed out in is the appended claims.

In the accompanying drawing, 1 and 2 represent two alternating current systems which are arranged to be interconnected by a frequency converter 3. This converter includes a synchronous machine 4 having a primary winding which is arranged to be connected to the system 2 by means of a suitable switch 5, and an asynchronous machine 6 having a' primarywinding which is arranged to beconnectedto the system 1 by means of a suitable switch '7. The rotors of the two machines '4 and 6 are mechanically connected together. The field winding of the synchronous machine 4 may be supplied with direct current in any suitable manner, examples of which are well known in the art.. As shown in the drawing, the field winding of the synchronous machine 4 is permai'iently connected across the brushes of a direct connected exciter 8. The asynchronous machine 6 is provided with a phase wound secondary wind- --1ng. I The frequency converter 3 is started by connecting the primary winding 01' the asynchronous machine 6 to the system 1 while the secondary winding is connected to a suitable starting resistor 10. The switch 7 which connects theprimary winding of the asynchronous machine 6 to the system 1 may be controlled in any suitable manner, examples of which are well known in the art. In order to simplify the disclosure we have shown it as a manually controlled device. The connection of the secondary winding of the asynchronous machine to the starting resistor 10 is controlled by suitable switching means whereby the'resistor is disconnected from the secondary winding after i the speed of the machine reaches a predetermined value. Any suitable speed responsive means such as a centrifugally operated switch, an undercurrent relay responsive to the startingcurrent, etc., examples of which are well known in' the art, ymay be employed to' effect the operation of the switching means when the machine reaches a predetermined speed. As shown in the drawing, a centrifugally operated switch 11 is provided for effecting the energization of the closing coil 12 of a switch 13 to effect the disconnection of the resistor iilfrom the secondary circuit of the asynchronous machine 6 whentthe speed of the machine increases above a predetermined value..

After the frequency converter 3 has been start- L ed, we provide in accordance with our invention an arrangement for automatically controlling, the speed of the asynchronous machine 6 so as to bring the synchronous machine4 and the system 2 into synchronism at which time the switch 5 is automatically closed to connect the primary winding of the synchronous machine 4 to the system 2.

For controlling the speed of the asynchronous machine 6, one modification of the so-called Scherbius controlis shown. The theory of operation of thisregulating apparatus is well known in the art and is fully set forth in the United States Letters Patent 1,306,594 and 1,778,599. In the modification shown in the drawing, the regulating apparatus includes two dynamo-electric machines 15 and 18 which have their rotors di-" rectly connected to the rotors of the machines'4 and 6. The regulating machine 15 is of the commutator type and the brushes 14 thereof are arranged to be, connected to the slip rings 22 of the machine Gwhen the speed thereof is above a predetermined value. The regulating machine 15 is also provided with two sets of field windings 16 and 17 which are excited by the other machine 18 which is a frequency converter of the well known ohmic drop exciter type. The frequency changer 18 has collector rings 19 which are arranged to be connected to the system 1 when the switch .7 is closed and two sets of brushes 20 and 21 which are arranged to be connected to'the windings 16 and 17 in'such a manner that the'windings 1'7 are energized in response to the voltages between the brushes 21 and the windings 16 are energized in response to the Voltages between corresponding brushes of thetwo sets of brushes 20.

and 21. A suitable brush shifting mechanism, in-

cluding a reversible motor '25, "is provided for shifting the brushes 20 and 21 on the commutator of the frequency converter 18 .so that the windings 16 and 1'7 of the machine 15 are exciteed in the desired manner. Sincethe construction of such a-brush shifting mechanism is well known in the art and one particular construction is disclosed in the aforesaid Letters Patent 1,778,595, the constructional details of this mechanism are not shown inthe drawing.

In accordance with our invention, after the regulating machine brushes 14 are connected to the secondary winding of the asynchronous machine 6 and before the switch 5 is closed, the brushes 20-and 21 of the frequency changer 18 are automatically controlled in response to the fre-v quency difference between the synchronous machine 4 and the system 2 so as to bring them into synchronism. When they are in synchronism, the

switch 5 is automatically closed andthen the brushes 20 and 21 are automatically controlled in response to the power transferred between the 7 examples of which are well! known in the'art,

may be provided for selectively controlling the operation of the brush shifting motor 25, 'As

shown, the frequency difference responsive means includes two single-phase synchronous motors 26 and 27 respectively connected to one of the primary phases of the-synchronous machine 4 and to one phase of the system 2. The two synchroe nous motors are arranged in any suitable manner so that the contacts 28 and 29 are closed when the frequency of the system 2 is higher than the frequency of thesynchronous machine 4 and the contacts 28 and 30 are closed when the frequency of the system 2 is lower than the frequency of the'synchronous machine 4. The contacts 28 and 29 control the circuit of a control relay 32 which, in turn, controls the circuits of thereversible motor 25 so that the brushes are adjusted in a manner to increasethe speed of the machines 4 and6. The contacts 28 and 30 control the circuit of a control relay 33which, in turn, controls the circuits of the reversible motor 25 so i that thebrushes 20 and 21 are adjusted in a manner to decrease the speed of the machines 4 and'6. A suitable interrupter 31 is also preferably provided in serieswith the contact 28 so that the circuit therethrough is only closed during a portion of each revolution thereof.

In'accordance with our invention, we also provide 'a suitable automatic synchronizer 35, examples of which are well known in the art, for effecting'the closing of the switch 5 between the synchronous machine 4 and the system 2 when a predetermined phase relation exists between the voltages of the system 2 and the synchronous machine 4. Since the details of such an automatic synchronizer form no part of our present invention, and furthermore they are old and well known in the art, we have shown the automatic synchronizer 35 schematically in order to simplifythe disclosure of the present invention. Preferably the automatic synchronizer, 35 is arranged to effect the closing of the switch'5 only when both the frequency difference and phase difference between the voltages of the synchronous machine 4 and" the system 2 are less than predetermined values. As shown, the automatic synchronizer 35 includes contacts 36 which, when closed, complete an energizing circuit for the closing coil 3'7 of the switch 5. The switch 5'in closing removes the, control of the brush shifting motor25 from the frequency difference responsive means 24 and places the motor'25 under the control of a suitable contact making waitmeter 38 which is connected in any suitable manner so that it is energized in response to the power flowing in the primary circuit of the synchronous machine 4. This contact making wattmeter 38 'is arranged to control the circuits of the control Pig relays 32 and 33 in such a manner that the amount of power transferred fromone system to the' other by the frequency converter 3 after the switch 5 is closed is, maintained at a predetermined value. c

In order that the power may be maintained at any desired value, the wattmeter 38 is preferably arranged in any suitable, manner, examples of means 24 operaive which are well known in the art, so that it can open and close its contacts in response to different values of power flowing between the system 2 andthe synchronous machine 4. Also a suitable reversing switch 39 is provided for reversing the proper connections of the wattrneter and the circuits of the control relays 32 and 33 so that the wattmeter may control the transfer or" power in either direcion between the two systems 1 and 2.

Suitable means are also 'providedfor effecting the movement of the brushes 20 and 21 to a predetermined position when the frequency converter 3 is shut down. includes-a limit switch 40 controlled by ihe positionof the brushes 20 and 21 and auxiliary con".- tacts 41 on the switch '7. q

The operation of the arrangement shown in the drawing is as follows: The frequency converter 3 is started by closing the switch 7 which connects the primary winding of the asynchronous machine 6 to the system 1, the secondary wind ing of the machine 6 being connected to the starting resislor 10 through the contacts of the switch 13, The asynchronous machine 6 then accelerates the frequency converter 3 andwhen it reaches a predetermined speed, the speed responsive device 11 closes its contacts and com-- pletes through the confacts 42 on switch '7 energizing circuitfor the closingcoil 12 of the switch 13. The switch 13 then operates to dis-- connect the starting resistor 10 from ihe second ary circuit of the asynchronous machine 6 and to connect'this secondary circuit to thebrushes 14 of the regulating machine 15. By closing its coniacts 43, the switch 13 also completes a locking circuit for the closing coil 12, thi locking circuit being independent of the contacts of the speed responsive device 11. By closing its contacts 44, the switch 13 also renders the'speed control ,4 into synchronismwith the system 2. If the As shown, this means to control the brushes 2O and 21 so as to bring the synchronous machine' speed of the synchronous machine 4 is too low,

the contacts 28 and 29 of the speed control means 24 are closedso that each time the circuit is completed through the interrupter 31 a circuit is {completed for the control relay 32 through the contacts 42 of switch 7, coniacts 44 of switch 13,

and contacts 50 of switch 5. The relay 32 by closing its contacts45 and 46 completes an energizing circuit for the brush shifting motor 25 so that the brushes are shifted to efiect an increase in the speed of the machi-nes 4 and 6. If the speed of the synchronous machine 4 is toohigh, the contacts 28 and 30 of the speed control means 24 are in engagement so that'each time a circuit is completed through the interrupter 31, an energizing circuit is completed for the control relay 33 through contacts 50 of switch 5, contacts 44 of switch 13 and contacts 42 of switch 7. The relay 33 by closing its'contacts 47 and 48 com pletes an energizing circuit for the brush shifting motor 25 so that the brushes 20 and 21 are shifted to effect a decrease in speed of the machines I the auxiliary contacts 42 on switch 7, contacts 44 of switch 13 and auxiliary'contacts 50 on switch 5. The closing of the switch 5 connects the primary winding of the synchronous machine 4'- to the system 2 so that the frequency converter is now interconnected between the two Systems. By closing its auxiliary contacts 51, the switch 5 completes a locking circuit for its closing coil 37, this locking circuit being independent of the automatic synchronizer contacts 36 and'the auxiiiary contacts 50 on the switch 5. 'By openingits contacts 50,- 52 and 53 and closing its contacts 54 the switch 5 removesthe brush shifting motor 25 fromthe control of the speed control means 24' and places it under-the control of the contact. making wattmeter 38.

When the switch 39 is in the position shown, the wattmeter 38 operates to maintain at a predetermined value the power flowing from the system 1 to the system 2 and when it is in its other position it maintains at a predetermined value the power flowing from the system 2 to the system 1. If the power flowing from the synchronous machine 4to the system 2 when the switch 39 is in the position shown decreases below a predetermined value, the wattmeter 38 closes its contacts Miami 57 so that a circuit is completed for the control relay 32 to eiTect the necessary change in the position of the brushes 20 and 21 to increase the power flowing from the synchronous machine 4'to the system 2 to the desired value. The circuit of the control relay 32 also includes the contacts 54 on the switch 5, contacts 44 on switch 13 and contacts 42 on switch '7. If the power flowing from the synchronous machine to the system 2 increases above this predetermined value, the wattmeter 38 closes its contacts 56 and 58 so that a circuit is completed through the contacts 42 on switch '7, contacts 44 on switch 13 and contacts 54 on switch 5 for the control relay 33. The control relay 33 then operates to shift the brushes in such a manner as to decrease to the desired value the power flowing from the synchronous machine to the system 2. When the switch 39 is in its other position, the wattmeter 38 controls in an obvious manner the circuits of the control relays 32 and 33 so that the brushes 20'and 21 are adjusted to maintain at a predetermined value thepowerflowing from the system 2 to the synchronous machine 4.

The frequency converter 3 is shut down by opening the switch '7. By opening its auxiliary contacts 42 the switch '7 interrupts thelocking circuits for the closing coils 12 and 3'7 of the switches 13 and 5 so that the starting resistor 10 is reconnected to the secondary winding of the asynchronous machine 6 and the synchronous machine 4 is disconnected from the system 2. By closing its auxiliary contacts 41, the switch 7 completes through the contacts of the limit switch 40: anobvious circuit for either the control relay 32 or the control relay 33 to restore the brushes 20 and 21 to their normal positions.

- While we have, in accordance with the Patent statutes, shown and described our invention as applied to a particular system and as embodying various devices diagrammatically indicated, changes and modifications will be obvious to those skilled in the art and we therefore aim in the appended claims to' cover all such changes and modifications as fall within the true spirit and scope of our invention. 1

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, an alternating current circuit, a synchronous machine, a phase wound asynchronous machine driving said synchronous machine, and means including an alternating currentsource ofexcitation controlled in accordance with the relative frequencies of said synchronous machine and said circuit for supplying alternating current of the proper frequency and magnitude to' the secondary winding of-said asynchronous machine to bring saidsynchronous machine substantially into synchronism with said circuit.

2.,In combination, an alternating current cir cuit, a synchronous machine, a phase wound asynchronous machine driving said synchronousmachine, means including an alternating current source of excitationcontrolled in accordance with the relative frequencies of said synchronous machine and said circuit for supplying alternating current. of the proper frequency and magnitude to the secondary winding of said asynchronous machine to bring said synchronousmachine substantially into synchronism with said circuit, and means controlled by the phase relation between the voltages of said synchronous machine and said circuit for connecting said synchroneus machine to said circuit when theyare substantially in synchronism.

3.In' combination, an alternating current circuit, a synchronous machine, a phase wound asynchronous machine driving said synchronousmachine, means including an alternating current source of excitation controlled in accordance with the relative frequencies of said synchronous machine and said circuit for supplying alternating current of the proper frequency and magnitude to the secondary winding of said asynchronous machine to bring said synchronous machine substantially into synchronism with said circuit, means controlled by thephase relation between the voltages of said synchronous machine and said circuit for connecting said synchronous machine to said circuit when they are substantially in synchronism, and means responsive to the connection of. said synchronous machine to said aircuit for controlling the alternating current supary circuit of said asynchronous machine of the same frequency as the frequency of said secondary circuit, and-means controlled in response to the relative frequencies of said synchronous machine and said other circuit for controlling said voltage applying means to bring said synchronous ma-' chine substantially into synchronism with said other circuit. V

5. In combination, two alternating current circuits, rotary transforming means for interconnecting said circuits including an asynchronous machine and a synchronous machine which have their rotors mechanically connected together, means for connecting the primary of said asynchronous machine to one Of said circuits, an alternating current exciter electrically connected to the secondary winding of said asynchronous machine, an ohmic drop exciter including movable brushes for supplying excitation to saidalternating current exciter at a frequency proportional to the slip frequency of said asynchronous machine, and means controlled in response to the relative "to the secondary winding of said asynchronous machine, an ohmic drop exciter including movable brushes for supplying excitation to said alternating current exciter at a frequency proportional tothe slip frequency of said asynchronous Inachine, means controlled in response to the relative frequencies of said synchronous inachineand said other circuit for adjusting said brushes to bring said synchronous machine substantially into synchronism with said other circuit, and means controlled by the phase relation between the voltages of said synchronous machine and said other circuit for connecting said synchronous machine to said other circuit when they are substantially in synchronism. I

7, In combination, two alternatingcurrent circuits, rotary transforming means for intercom necting said circuits including an asynchronous machine and a synchronous machine which have their rotors mechanically connected together, means for connecting the primary of said asynchronous machine to one of said circuits, an Ell-2 ternating current exciter electrically connected to the secondary winding of said asynchronous machine, on ohmic drop exciter including movable brushes for supplying excitation to said alternating current exciter at a frequency proiportional to the slip frequency of said asynchronous machine, means controlled in response to the relative frequencies of said synchronous machine and said other circuit for adjusting said brushes to bring said synchronousmachine substantially into synchronism with said other cir cuit, means esponsive to the power flowing through the armature of said synchronous machine, and means controlled by the phase relation between the voltages of said synchronous 'machine, and said other circuit for connecting said synchronous machine to said other circuit 'when they are substantially in synchronisin and for placing said brushes under the controlof said power responsive means after said synchronous machine is connected to said other circuit.

8. In combination, two alternating current circuits, rotary transforming means for interconnecting said circuits including an asynchro nous machine and a synchronous machine which have their rotors mechanically connected together, means forconnecting the primary of said asynchronous machine to one of said circuits, an alternating current exciter, an ohmic drop exciter including movable brushes for supplying excitation to said alternating current exciter at a frequency proportional to the slip-frequency of saidasynchronous machine, means controlled by the relative frequencies of said synchronous machine and said other circuit, and means controlled, by the speed of said asynchronous machine for connecting said alternating current means for connecting the primary of saidasynchronous machine to one of said circuits, an alternating current exciter, an ohmic drop exciter including movable brushes for supplying excita-v tion to said alternating current. exciter at a frequency proportional to the'slip frequency of said asynchronous machine, means controlledby therelative frequencies of said synchronous machine and said other circuit, means controlled by the speed of said asynchronous machine for connecting said alternating current 'exciter to the secondary winding of said asynchronous machine and for placing said movable brushes under the control of said frequency controlled means, and means controlled by the phase relation between the voltages of said synchronous machine and said other circuit for effecting the connection of said synchronous machine to said other circuit and the removal of the control of said brushes from said frequency controlled means.

10. In combination, two alternating current circuits, rotary transforming means for interconnecting said circuits including an asynchronous machine and a synch onous machine which have their rotors mechanically connected together, means for connecting the primary of said asynchronous machine to one of said circuits, an alternating current exciter, an ohmic drop exciter including movable brushes for supplying excitation to said alternating current exciter at a frequency proportional to the slip frequency of said asynchronous machine, means controlled by the relative frequencies of said synchronous machine and other circuit, means controlled by the speed of said asynchronous machine for connecting said alternating current exciter to the secondary winding of said asynchronous machine and for placing said movable brushes under the control of said frequency controlled means, means responsive to the power iiowingthrough the armature of said synchronous machine, and means controlled by the phase relation between the voltages of said synchronous machineand said other circuit for effecting the connection of said synchronous machine to said other circuitand for placing saidbrushes under.

the control of said power responsive means after said synchronous machine is connected to said other circuit. 6

11. In combination, an alternating current circuit, a synchronous machine, a phase wound 

